Bisulfide

It is an important chemical reagent and an industrial chemical, mainly used in paper pulp industry (Kraft process).

Properties

A variety of salts are known, including sodium hydrosulfide and potassium hydrosulfide. Ammonium hydrosulfide, a component of "stink bombs" has not been isolated as a pure solid. Some compounds described as salts of the sulfide dianion contain primarily hydrosulfide. For example, the hydrated form of sodium sulfide, nominally with the formula Na₂S · 9 H₂O, is better described as NaSH · NaOH · 8 H₂O.

Aqueous bisulfide absorbs light at around 230 nm in the UV–visible spectrum. Using this approach, bisulfide has been detected in the ocean and in sewage.

Basicity

At physiological pH, hydrogen sulfide is almost fully ionized to bisulfide (HS⁻). Therefore, in biochemical settings, "hydrogen sulfide" is often used to mean, bisulfide. Hydrosulfide has been identified as the third gasotransmitter along with nitric oxide and carbon monoxide.

It has a pK_a of 6.9:

Reactions

Upon treatment with an acid, bisulfide converts to hydrogen sulfide. Oxidation of bisulfide gives polysulfides and eventually sulfate. When anstrongly heated, alkali bisulfide salts decompose to produce sulfide salts and hydrogen sulfide. 2NaHS → H₂S + Na₂S

When treated with metal salts, bisulfide gives the corresponding sulfide:

2NaHS + M²⁺→ MS + 2 Na⁺ (M = Ni(II), Pb(II), Cd(II), etc)

This conversion is the basis of some schemes in qualitative inorganic analysis.

Under specific conditions, SH⁻ forms some complexes containing SH ligands. Examples include [Au(SH)₂]⁻ and (C₅H₅)₂Ti(SH)₂, derived from gold(I) chloride and titanocene dichloride, respectively.